Everything you need to know about Ultra Wideband in the iPhone 12 and HomePod mini

Alongside the launch of its iPhone 12 range of smartphones, Apple introduced a number of other products over the course of multiple special events. The appearance of Ultra Wideband support in the HomePod mini, as well as the Apple Watch Series 6, generated more conversation about the technology and its potential future use by the company.

Some may still be bewildered by what Ultra Wideband actually does, and how it can benefit them down the line. Outside of Apple’s explanation that it can be used for some location tracking, the company hasn’t really offered much in the way of an explanation for Ultra Wideband in practice, outside of AirDrop prioritization.

In this article, we aim to demystify Ultra Wideband.

Commonly referred to as UWB, Ultra Wideband is a wireless protocol for communications, which functions using radio waves. At its most basic, it can be used to transmit messages between devices, making it somewhat analogous to Bluetooth or Wi-Fi.

As it has potential applications for personal area network communications, namely allowing devices on a person to communicate with each other, there is a lot of crossover with the more established Bluetooth. However, the way it operates means it can offer some more functionality the other two communications types cannot provide.

The main feature it enables is highly-accurate location tracking, with devices using UWB potentially able to identify the distance and even the location of other hardware relative to itself to within a few inches. This means it has potential uses for device tracking services, like an enhanced form of the Find My app.

Apple’s iPhone 11 product page detailing the inclusion of the U1 chip in 2019.

While it has some industrial purposes, including radar systems, medical imaging, and even tested to handle signaling on the New York City Subway, the main use of the technology for consumers is still likely to be inter-device communications and short-range location tracking.

As an idea, UWB has been around for quite some time. Only relatively recently has it risen in prominence, mainly due to Apple’s inclusion of the technology in the iPhone 11.

The FiRa Consortium, which includes Samsung, Oppo, Xiaomi, and other firms in its membership, was formed in 2019 to encourage the creation of UWB for consumer devices that works across platforms, such as between different models of smartphone. While the group exists, it so far doesn’t count Apple as a member, and it is unclear if Apple’s implementation will work with FiRa’s version in the future.

Like other radio-based communications systems, UWB relies on a combination of transmitters and receivers on devices. While Wi-Fi and Bluetooth use a relatively narrow frequency ranges to handle communications between devices, UWB does things completely differently.

As the “Ultra Wideband” name suggests, UWB does away with narrow ranges and instead transmits data across a far larger frequency band. While a typical Wi-FI channel width may be 20MHz, 40MHz, or 80MHz in size, UWB instead uses a bandwidth range of 500MHz or more for its transmissions.

UWB typically can afford to do this because it operates in a large band that isn’t typically used for other types of communications, which the FCC authorized the range of 3.1GHz to 10.6GHz for unlicensed use. For Apple’s U1 chip, which is used for Apple’s own Ultra Wideband applications, a teardown by TechInsights indicated it transmitted on two frequencies: 6.24GHz and 8.2368GHz.

The U1 chip in the iPhone 11 Pro Max [via TechInsights]

An unusual characteristic of UWB is that it is a pulse-based system, one that repeatedly blasts out signals then turns off before repeating. While each pulse can take up the entire range of bandwidth assigned to it, the extremely short transmission times of each pulse, as well as the relatively low-power nature of consumer-oriented UWB, makes it highly unlikely for it to interfere with other systems in the same ranges.

The use of such large bands means the signal could easily be used to transmit data. Given that it is capable of transmitting over a billion pulses per second, and uses multiple pulses for each bit of encoded data, this can equate to a speed of hundreds of megabits per second under ideal conditions

This isn’t quite Wi-Fi network levels of speed. It is still quite a lot for communications outside of user-driven large file transfers.

The regulator-mandated low power levels for broadcast combined with the more fragile nature of higher-band transmissions means the general utility range isn’t far, typically up to 30 feet away, and so not ideal for such communications in the first place.

The pulse-based nature of Ultra Wideband lends itself to location tracking in a few ways. For a start, by regularly sending out a pulse of data, it can enable other nearby devices to know it exists, or vice versa if it receives a pulse from another device.

The use of UWB and its wide range of frequencies used also enables devices to perform Time of Flight (ToF) calculations, namely how long it takes to get a response, which provide a far more useful data point: how far apart the devices are located.

By using such a wide frequency range, this practically enables the system to beat multipath propagation, namely instances where radio waves take multiple paths to reach a destination, such as echoing off surfaces. Since some of the frequencies used in the pulse are highly likely to make it to the intended recipient directly with line of sight, calculations can be based on them and not the slower diverted signals on other frequencies, resulting in a more accurate calculation.

An Apple illustration of UWB being used for relative location-based gaming, in this case multiplayer Pong.

One iPhone sends a packet of data out to a second iPhone, in a task known as “ranging.” The second device receives it, and sends a response back to the first, which is then received, with all of the times of receiving and transmission recorded.

The first device can then send a third packet of data to the second, containing a device ID, the timestamp of sending the first packet, the timestamp of when the first device received its response, and the time the third packet was sent. This is enough data for the second device to determine how far away the two devices are from each other.

Since the second device has timestamps for receiving and sending packets, similar data points can be sent over, which informs the first device of the range as well.

As it is also possible for UWB radios to determine the angle of an inbound signal, this can also enable it to determine a direction the device is located in relation to it. Combine that with the distance calculation, and an overall relative position can be determined, and at a higher degree of accuracy than other methods.

For example, it is possible to determine the location of a device using Wi-Fi signals to within about 10 feet, while GPS with GLONASS can get to within 6 feet. Bluetooth can feasibly get to within about 10 feet for distance for devices using Bluetooth 5.0 or later, but Bluetooth 5.1 introduces more directional sensing capabilities that could enable location tracking to within a few inches, once the technology becomes more commonplace.

UWB’s accuracy can pin a device down to within a foot at worst, but generally to within a few inches. Accuracy will depend on a few factors, such as distance and line of sight between devices.

While the idea of UWB has been around for quite some time, it has only become a consumer concern since late 2019, when Apple included the technology in the iPhone 11 range, including the iPhone 11 Pro and iPhone 11 Pro Max. In those models, Apple introduced the U1 chip, which is used solely for UWB communications.

At the time, Apple offered a reason for its use in AirDrop, in that it could be used to prioritize the list of devices that a file could be shared to. By pointing the iPhone at another iPhone, that device jumped to the top of the sharing list.

The HomePod mini uses UWB for device proximity features.

Outside of iPhones, only two other devices in Apple’s range have U1 chips, with the Apple Watch Series 6 and HomePod mini both equipped with Ultra Wideband support. However, Apple hasn’t really outlined any reason for U1 to exist in the models. Though the HomePod mini enables proximity-based Handoff by drawing an iPhone close to it, this is also available without UWB on the HomePod, but Apple does say it is used specifically for “device proximity” functionality on the mini.

In terms of what to expect from UWB in the future, Apple has been relatively quiet about what’s on the horizon, though unlike other elements of its ecosystem, it’s not been entirely silent.

In June, Apple introduced a “Nearby Interactions” developer framework for U1-equipped devices, enabling developers to create apps that take advantage of relative direction and distance data. As part of its documentation, Apple proposed a ride-share app that allows a driver and a passenger to find each other easily, and an augmented reality water balloon fight.

Apple is also believed to be considering some non-iPhone usage for UWB as well, with the often-rumored “AirTags” being a prime example.

‘AirTags’ are rumored to be a device-tracking tag powered by UWB [image via Jon Prosser/@CConceptCreator]

Thought to be similar in concept to Tile tracking tags, “AirTags” consist of a small round disc that is equipped with Bluetooth and UWB radios. The idea is to attach them to items you want to track, then to use the Find My app to relocate them.

The Find My app is also believed to provide not only the geographical location of the tag, but also will take advantage of augmented reality to display the nearby location of the tag overlaid on a live video feed from an iPhone’s camera.

The idea is that an “AirTag” left in the world will repeatedly ping out using UWB, which could be picked up by nearby iPhones equipped with the U1 chip that happen to be in the area. These iPhones would share the location data for where it was when it detected the UWB broadcast, which can be provided to the tag’s owner via the app.

The existence of the U1 chip in the HomePod mini suggests there could be some form of smart home functionality on the way, potentially involving HomeKit. For example, Apple could enable a feature where UWB is used by a new HomeKit device to work out which “Room” it should be installed to based on the nearby presence and relative location of other products.

It could also be feasible to use a detection of an iPhone in a room to apply generic verbal commands such as “turn on the lights” to apply to just that room, and to automatically turn them on and off as the user moves between rooms. Such hyperlocal geofencing opens up a world of smart home interaction possibilities.

Of course, this does depend on Apple adding U1 to even more products and potentially enabling other devices to interact with its UWB implementation. Given the U1’s expansion from iPhones to the Apple Watch and the HomePod mini, it seems highly plausible Apple will be doing just that.